So I read a while back that if you plant a sapling, then surround it in the four cardinal directions with other blocks (usually dirt or gravel because they're easy to remove) then when the tree grows, since it can't "sprout" leaf blocks at a normal height due to the other blocks, it will just keep going until it reaches the end of the blockage and the leaf blocks will appear that high up, with log blocks all the way from the ground to there, making it possible to manually make extremely tall trees.

I want to build a large treehouse, so I'm starting with a 3x3 base of trees all in one large block to make one thick megatree for the base. So far I've planted five of the saplings (can't plant the other 4 yet because I have to fill those spaces with dirt for now) and surrounded them with dirt. The tops are obviously open so they can still get sunlight, and because I want to make a sort of lookout tower/lighthouse on top, there's roughly ~20 spaces between the highest spot of dirt and the invisible build limit in the sky, so the trees have room to grow.

I build a little catwalk of dirt away from it (so I wouldn't be choked to death by leaves suddenly spawning on me), set a torch nearby (but still out of the way) so mobs wouldn't spawn with me up there, and simply waited.

I left the game running with nothing else going on my computer, went to the living room and hung out with my roommate for... I'd say two or three hours. I checked back periodically and nothing. I'd planted a bunch of other saplings on the ground below (I want my treehouse to be in the middle of a dense forest, so I'm planting more saplings in a worldgenned forest to make it thicker), and all of those in my view distance (which was set to far) had grown (we're talking like 30+ and I couldn't see a single sapling), but none of my megatree-to-be had sprouted yet.

Did this get patched out? Was it just a rumor that was never true to begin with? Do supertrees just take longer to grow?

Sometimes they take a really long time to grow. I've grown a few of my own super-trees on my map and some of the saplings still refuse to do anything. You may just need to give them more time, a few hours certainly won't be enough for some of them. Also make sure that there is at least four blocks of clearance above thema and that you are in the same chunk for them to grow.

I didn't use the dirt method to grow mine. I just let one sapling grow into a tree, then surrounded that tree with more saplings. That way the tree is entirely filled with wood (in order to be carved out for a tree fort of course!).

This is the first tree I grew. It was in my garden because it was originally meant to be a wood harvesting area. It started as an experiment once I realized that the trees grew larger when next to other trees. This one has a solid 3x3 trunk:

This is the second one I grew. I am still in the process of setting it all up, but I plan to make a treehouse in this one and add a waterfall off of the little island. The platform is temporaryfor now. The trunk on this one is larger than the other one. It has an extra three trees per face:

Somewhat randomly, (if I'm not mistaken), if you light the top of a log block on fire, it will not be consumed with flame, but rather will burn forever. I've noticed that if you light the sides of a log block it will definitely be destroyed, but more often than not, if you only light the top, it should work.

Personally, I find that many of the bugs and physics exceptions are what make the game interesting and nuanced. I'm not sure how I feel about the fact that Notch is going to eventually plug all the holes and introduce new challenges. Torches that can burn out? Lord, no.

Well from what I've read, when/if Notch changes torches to burn out, he will replace their current identifier to identify whatever permanent source replaces them. I would probably just start making the new light source and only use torches for short cave expeditions or something, and set up lanterns(?) if I decide to make it a more permanent operation.

Just plant a tree, let it grow, put a dirt block on top of it, plant another tree, replace the dirt with a wood block after the second tree on top grows (actually i'm not sure if this part will work, anyone know if the tree will die or something without dirt?) and keep doing it until desired height?

I'm pretty sure trees are fine if you dig under them. The log blocks just act like log blocks, and leaf blocks should only disappear when nothing is supporting them from beneath AND they have no attached log block at their level. So if all you do is remove the one dirt block and replace it with a log it should be fine.

Anywho I knew that would work, but it would just take so much longer so I was trying to avoid it. But if this doesn't work then I guess I'll have to. :/ Thanks for answering!

From my observation, this still exists. Here's how mine ended up happening on accident:

I planted a 5 x 5 grid of saplings, with two spaces between each sapling. On the first go round, with all the trees having grown, every tree was normal. I harvested on edge of the farm and then replanted 5 saplings. What I noticed was that the leaves that had been attached to the trees I had cut down were still "alive". I understand that they remain "alive" as long as they touch another leaf block (or tree) that is attached to a tree.

Anyway, so the 5 saplings I planted grew eventually, but they grew up and above the "leaf line" of the tree that was there before. This seems to continue every time I harvest a few trees and replant.

Hope that gives you the info you need to get your problem fixed. Perhaps you shouldn't try to force the megatrees and let them happen naturally?

I can definitely tell you that you can grow trees on top of one another by placing a dirt block on top of a tree and waiting a while. You can also then remove that dirt block and add wood... the tree won't die. I tested this myself and currently have 4 or 5 "super trees." They do seem to take abnormally long to grow, however. And I'm still working on getting two of the large-style (branching) trees to grow on top of one another. Just takes time.

I don't know exactly how tall you can get a single tree to grow at one time, but placing a column at one of the 8 squares around the sapling will make it grow much larger every time. I usually place a 6-8 block high column of dirt (or whatever) next to the sapling and always get a supertree.

Put some torches around the tree as well so it will grow at night and if you still don't have anything after a few minecraft days, rip that sapling out of the ground and replant it. I had one sapling that didn't grow after a week in game. I replanted it and had a nice large tree the next day. The grow time is just random and sometimes takes forever.

I haven't tested to see if you can grow a tree like 40 blocks tall in one go though. It seems like the taller you try to grow them at one time, the longer it takes pretty much every time. It would probably be easier for you to grow it 6-8 blocks tall and then plant a sapling in the top of that tree after it's grown. I'm pretty sure it will take much less time to grow as high as you want it to grow.